As described, for example, in the paper "An Integrated Circuit Device Encapsulants," by C. P. Wong, included in the book Polymers for Electronic Applications, edited by J. H. Lai, CRC Press, Inc., Boca Raton, Fla., 1989, pp. 63-92, organic materials such as silicone resins are coming into increased use for electronics packaging, encapsulation and interconnection. Many of these materials have the appropriate thermal stability, dielectric properties, chemical stability and resistance to atmospheric deterioration needed for use either as dielectric layers or as encapsulants. Such materials are particularly useful as dielectric layers and encapsulants for hybrid integrated circuits (HICs) in which a silicon chip is mounted on a ceramic substrate having a metal conductive pattern on one surface.
A particularly good dielectric layer for use with high voltage HICs is a piolymethylphenylsiloxane containing about sixty-five percent by weight of a silica filler which will be described more completely later. This material resists applied high voltages without breakdown, has good adhesive qualities and therefore is useful as a dielectric layer between a high-voltage silicon chip and a ceramic substrate upon which metal conductors have been defined. Unfortunately, examination of this material by a scanning electron microscope (SEM) shows microcracks in the material after cure. Such cracks limit the long-term reliability of the material for use either as an electron device encapsulant or dielectric layer.